Liquid crystal projector, and projection lens unit, optical unit and cooling system for the same

ABSTRACT

A liquid crystal projector comprises an illuminating optical system including a light source, a color separating optical system for separating illuminating light rays emitted by the illuminating optical system into light rays of three colors, a projection lens unit comprising a projection lens, a cross dichroic prism disposed near a light receiving end of the projection lens, and a plurality of liquid crystal panels arranged around the cross dichroic prism, and a light source power supply for supplying power to the light source. The projection lens unit, the color separating optical system, the illuminating optical system and the light source power supply are arranged in that order. The liquid crystal projector has an outside size in a horizontal plane of 263 mm by 318 mm or below. The liquid crystal panels have a display screen size of 0.9 in. A cooling fan for cooling the plurality of liquid crystal panels is disposed beside the projection lens.

This is a continuation application of U.S. Ser. No. 10/422,952, filedApr. 25, 2003 (now U.S. Pat. No. 6,824,273), which is a continuationapplication of Ser. No. 09/791,702, filed Feb. 26, 2001, now U.S. Pat.No. 6,783,245, which is a continuation application of U.S. Ser. No.09/195,900, filed on Nov. 19, 1998, now U.S. Pat. No. 6,290,360.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal projector fordisplaying a picture on a screen by projecting light rays emitted by alight source onto three liquid crystal panels and transmitted by thethree liquid crystal panels, and a projection lens unit, an optical unitand a cooling system to be employed in the liquid crystal projector.

2. Description of the Related Art

A prior art liquid crystal projector provided with three liquid crystalpanels is disclosed in, for example, JP-A No. 6-289392. This prior artliquid crystal projector comprises, as principal components, a lightsource, a cold mirror, a blue light reflecting dichroic mirror(hereinafter referred to as “B light reflecting dichroic mirror”), agreen light reflecting dichroic mirror (hereinafter referred to as “Glight reflecting dichroic mirror”), image reflecting mirrors, ared-light liquid crystal panel (hereinafter referred to as “R liquidcrystal panel”), a green-light liquid crystal panel (hereinafterreferred to as “G liquid crystal panel”), a blue-light liquid crystalpanel (hereinafter referred to as “B liquid crystal panel”), a combiningdichroic prism and a projection lens. Light rays emitted by the lightsource are divided into R, G and B light rays by the light transmittingand reflecting agencies of the cold mirror, the B light reflectingdichroic mirror and the G light reflecting dichroic mirror, the lightrays are reflected by the image reflecting mirrors toward the R, G and Bliquid crystal panels. The light rays traveled through the R, G and Bliquid crystal panels are combined by the dichroic prism and a colorpicture is projected through the projection lens in an enlarged colorpicture on a screen.

Such a known, commercialized liquid crystal projector employs three 1.3in. liquid crystal panels. is formed in a compact construction and iscapable of displaying pictures in a high definition.

The foregoing liquid crystal projector is provided with a cooling systemfor suppressing the temperature rise of the liquid crystal panels.

Referring to FIG. 1 showing a known liquid crystal projector in a sideview, a cooling fan 81 (an axial fan in this liquid crystal projector)is disposed below three 1.3 in. liquid crystal panels (only liquidcrystal panels 14 and 18 are shown) to blow air toward the liquidcrystal panels including the liquid crystal panels 14 and 18 to suppressthe temperature rise of the liquid crystal panels including the liquidcrystal panels 14 and 18. Since the liquid crystal panels including theliquid crystal panels 14 and 18 are exposed directly to air delivered bythe cooling fan 81, the liquid crystal panels including the liquidcrystal panels 14 and 18 can effectively cooled. In FIG. 1, indicated at27 is a projection lens.

The outside size in a horizontal plane of this liquid crystal projectorprovided with the three 1.3 in. liquid crystal panels excluding aprojecting part of the projection lens projecting from a case is 245 mmby 329 mm, and the overall outside size in a horizontal plane of theliquid crystal projector including the projecting part of the projectionlens is 245 mm by 380 mm. Such a large overall outside size of theliquid crystal projector is a problem in storing and carrying the liquidcrystal projector, and the reduction of the overall outside size of theliquid crystal projector has been desired.

The inventors of the present invention examined a concept aboutminiaturization necessary to realize a liquid crystal projector morecompact than the prior art liquid crystal projector and found that aliquid crystal projector provided with three liquid crystal panels mustbe formed in the smallest possible outside size suitable for storing theliquid crystal projector in a prevalently used storage cabinet and forcarrying the same in a prevalently used carrying case.

The known liquid crystal projector shown in FIG. 1 has a height L2 equalto the sum of the height of a part including the projection lens 27 andthe liquid crystal panels 14 and 18, and the height of the cooling fan81. The liquid crystal projector has a dead space under the projectionlens 27, which increases the overall height of the liquid crystalprojector.

SUMMARY OF THE INVENTION

Accordingly, it is a first object of the present invention to provide aliquid crystal projector of an outside size capable of being stored in aprevalently used storage cabinet and of being carried in a prevalentlyused carrying case.

Another object of the present invention is to provide a liquid crystalprojector having a small height and formed in a compact construction.

A third object of the present invention is to provide a projection unitand an optical unit effective in forming a liquid crystal projector in acompact construction.

A fourth object of the present invention is to provide a cooling systemcapable of efficiently cooling a liquid crystal projector.

With the foregoing objects in view, the present invention provides aliquid crystal projector having a size in a horizontal planesubstantially equal to an A4 folder size, i.e., the size of folders forholding papers of the trimmed sheet size A4. The A4 folder size is 263mm by 318 mm. The liquid crystal projector of the present inventionsubjects light rays emitted by a light source to color separation todivide the light rays, projects the divided light rays on a first liquidcrystal panel, a second liquid crystal panel and a third liquid crystalpanel, combines the light rays traveled through the first, the secondand the third liquid crystal panel, and projects the combined light rayson a screen through a projection lens. The outside size in a horizontalplane of the liquid crystal projector is the outside size of a caseserving as a housing for the liquid crystal projector. The outside sizein a horizontal plane of the liquid crystal projector may be the sum ofthe size of the case and that of a part projecting from the case. Thesize of the first, the second and the third liquid crystal panel is 0.9in. or below. The distance between the display surface of the liquidcrystal panel disposed substantially perpendicularly to the optical axisof the projection lens and the extremity of the projection lens is about146 mm or below. The liquid crystal projector is provided with a colorcombining optical system including a cross dichroic prism for colorcombination. The cross dichroic prism has a size in a horizontal planeof 32 mm by 32 mm or below.

A liquid crystal projector according to the present invention comprisesa color separation optical system comprising a cross dichroic prism, anda first dichroic mirror, a second dichroic mirror, a first mirror, asecond mirror and a third mirror arranged around the cross dichroicprism, an illuminating system comprising a light source, a polarizingdevice and an optical integrating means, liquid crystal and a projectionlens unit comprising a light source power supply for supplying power tothe light source, and a projection lens unit comprising a plurality ofliquid crystal panels, a cross dichroic prism and a projection lens, inwhich the projection lens unit, the color separating optical system, theilluminating optical system, and the light source power supply arearranged in that order.

A liquid crystal projector according to the present invention comprisesa color separating optical system comprising a first dichroic mirror, asecond dichroic mirror, and a first mirror, a second mirror and a thirdmirror arranged around a cross dichroic mirror, an illuminating opticalsystem comprising a light source, a polarizing device, and an opticalintegrating means, a light source power supply for supplying power tothe light source, and a projection lens unit comprising a plurality ofliquid crystal panels, a cross dichroic prism and a projection lens, inwhich the combination of the projection lens unit and the colorseparating optical system, the illuminating optical system and the lightsource power supply are arranged in that order. An exhaust fan isdisposed near the light source. A cooling fan and a duct for guidingcooling air delivered by the cooling fan to the first, the second andthe third liquid crystal panel are disposed beside the projection lens.

A projection lens unit according to the present invention comprises aprojection lens, a cross dichroic prism disposed on the light receivingside of the projection lens, first, second and third liquid crystalpanels, and a structural means for arranging the first, the second andthe third liquid crystal panel around the cross dichroic prism with thesecond liquid crystal panel set substantially perpendicularly to theoptical axis of the projection lens, in which the distance between thedisplay surface of the second liquid crystal panel and the extremity ofthe projection lens is about 146 mm or below, and the size in ahorizontal plane of the cross dichroic prism is 32 mm by 32 mm.

An optical unit according to the present invention comprises anilluminating optical system including a light source, a color separationoptical system for separating light rays received from the illuminatingoptical system into light rays of three colors, first, second and thirdliquid crystal panels which receive the light rays of three colors,respectively, and a cross dichroic prism for combining light raystraveled through the first, the second and the third liquid crystalpanel, in which the size of the display screen of the first, the secondand the third liquid crystal panel is 0.9 in. or below and the size in ahorizontal plane of the cross dichroic prism is 32 mm or below by 32 mmor below.

A liquid crystal projector according to the present invention comprisesa housing, a first cooling system having a sealed duct including liquidcrystal panels, a second cooling system disposed inside the housing tocool the duct from outside, in which the liquid crystal panels arecooled directly by the first cooling system and are cooled indirectly bythe second cooling system. The first cooling system is provided with acooling fan. The size in a horizontal plane of the liquid crystalprojector is nearly equal to or below the A4 folder size.

A liquid crystal projector according to the present invention comprisesa plurality of cooling fans for cooling liquid crystal panels, in whichat least one of the cooling fans is disposed beside the projection lens.One of the plurality of cooling fans is used specially for cooling theliquid crystal panels. The cooling fan specially for cooling the liquidcrystal panels has a cooling duct divided into a plurality of sectionsso that cooling air flows toward the G liquid crystal panel at avelocity or a flow rate greater than that at which cooling air flowstoward the rest of the liquid crystal panels. One of those cooling fansis a centrifugal fan.

A cooling system according to the present invention comprises aplurality of liquid crystal panels, a cooling fan, a duct fordistributing a cooling fluid delivered by the cooling fan to theplurality of liquid crystal panels, and a plurality of guide membersdisposed in the duct to adjust the velocity or the flow rate of thecooling fluid flowing to each of the liquid crystal panels. The guidemembers adjust the flow of the cooling fluid so that the cooling fluidflows toward one of the liquid crystal panels at a velocity or a flowrate greater than that at which the cooling fluid flows toward the otherliquid crystal panel. The duct is extended between the cooling fan andthe plurality of liquid crystal panels. The duct is formed so as to blowthe cooling fluid upward from below the plurality of liquid crystalpanels. The duct may be extended from the cooling fan to the pluralityof liquid crystal panels and from the plurality of liquid crystal panelsto the cooling fan.

A projection lens unit according to the present invention comprises aprojection lens, a cross dichroic prism disposed on the light receivingside of the projection lens, first, second and third liquid crystalpanels disposed around the cross dichroic prism, a cooling fan disposedbeside the projection lens, a duct for carrying a cooling fluiddelivered by the cooling fan to the first, the second and the thirdliquid crystal panel, and a plurality of guide members disposed in theduct to adjust velocities or flow rates at which the cooling fluid flowstoward the first, the second and the third liquid crystal panel,respectively.

An optical unit according to the present invention comprises anilluminating optical system including a light source, a color separatingoptical system for separating light rays received from the illuminatingoptical system into light rays of three colors, a cross dichroic prism,first, second and third liquid crystal panels arranged around the crossdichroic prism, a cooling fan, a duct for carrying a cooling fluiddelivered by the cooling fan toward the first, the second and the thirdliquid crystal panel, and a plurality of guide members disposed in theduct to control velocities or flow rates at which the cooling fluidflows toward the first, the second and the third liquid crystal panel,respectively.

A cooling system according to the present invention is capable ofoptionally regulating velocities and flow rates at which air deliveredby a cooling fan flows toward a plurality of liquid crystal panels sothat the temperature rise of each of the plurality of liquid crystalpanels is limited to the lowest possible extent.

The velocities and the flow rates are controlled so that the flow rateand the velocity at which air flows toward the G liquid crystal panelare the highest and the flow rate and the velocity at which air flowstoward the R liquid crystal panel are the lowest.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a prior art liquid crystal projector;

FIG. 2 is a schematic plan view of a liquid crystal projector in a firstembodiment according to the present invention;

FIG. 3 is a schematic plan view of assistance in explaining a projectingpart in a liquid crystal projector according to the present invention;

FIG. 4 is a schematic plan view of a liquid crystal projector in asecond embodiment according to the present invention;

FIG. 5 is a schematic plan view of a liquid crystal projector in a thirdembodiment according to the present invention;

FIG. 6 is a schematic plan view of a liquid crystal projector in afourth embodiment according to the present invention;

FIG. 7 is a schematic side view of a part of the liquid crystalprojector around liquid crystal panels;

FIG. 8 is a perspective view of a cooling system included in the liquidcrystal projector of FIG. 6;

FIG. 9 is a perspective view of the cooling system included in theliquid crystal projector of FIG. 6;

FIG. 10 is a bottom perspective view of the cooling system included inthe liquid crystal projector of FIG. 6;

FIG. 11 is a schematic plan view of a liquid crystal projector in afifth embodiment according to the present invention; and

FIG. 12 is a schematic plan view of a liquid crystal projector in asixth embodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings.

Referring to FIG. 2 showing a liquid crystal projector in a firstembodiment according to the present invention in a schematic plan view,light rays 2 emitted by a discharge lamp 1, i.e., a light source, arereflected by a parabolic lamp reflector 3, travel through a lens 4, alens 5, a polarizing device 6, a first lens array 7, a mirror 8 and asecond lens array 9, and fall on a dichroic mirror 10. The dichroicmirror 10 allows R light rays 11 to pass through and reflects G and Blight rays 12. The R light rays 11 are reflected by a mirror 13 towardan R liquid crystal panel 14. The G and B light rays 12 fall on adichroic mirror 15 which reflects the G light rays and allows the Blight rays to pass through. The G light rays 16 are reflected by thedichroic mirror 15 toward and fall on a G liquid crystal panel 18. The Blight rays 17 are reflected by mirrors 19 and 20 toward and fall on a Bliquid crystal panel 21. R transmitted light rays 22 traveled throughthe R liquid crystal panel 14, G transmitted light rays 23 traveledthrough the G liquid crystal panel 18 and B transmitted light rays 24traveled through the B liquid crystal panel 21 are combined for colorcombination by a cross dichroic prism 25, and composite color light rays26 are projected through a projection lens 27 on a screen, not shown.

An exhaust fan 28 for cooling the discharge lamp 1 is disposed near thedischarge lamp 1 and the lamp reflector 3 to discharge hot air 30 heatedby heat generated by the high-temperature discharge lamp 1, i.e., thelight source, from a case 29 in order that the component parts of theliquid crystal projector may not be affected by heat generated by thedischarge lamp 1. A lamp power supply 31 is disposed near the dischargelamp 1. Suction fans 46 and 47 suck ambient air into the case 29. InFIG. 2, indicated at 48 and 49 are connectors, at 54 is an electricalpart, and at 55 is a wiring board.

In the first embodiment, the first dichroic mirror 10, the seconddichroic mirror 15, the first mirror 13, the second mirror 19 and thethird mirror 20 included in a color separating optical system arearranged around the cross dichroic prism 25. An illuminating opticalsystem is designed for efficient use of illuminating light and comprisesthe discharge lamp 1, the lamp reflector 3, the lens 4, the lens 5, thepolarizing device 6, and an optical integrating means including thefirst lens array 7, the mirror 8 and the second lens array 9. The lamppower supply 31 for supplying power to the discharge lamp 1 is disposedadjacent to the discharge lamp 1.

In the first embodiment, the projection lens 27, the cross dichroicprism 25, the color separating optical system, the illuminating opticalsystem and the lamp power supply 31 are arranged in that order.

The projection lens 27 is disposed in the case 29 so that the projectionlens 27 is contained entirely in the case 29 or a part of the projectionlens 27 projects outside from the case 29. The outside size in ahorizontal plane of the liquid crystal projector in the first embodimentincluding a projecting parts is not greater than that of an A4 folder.The outside size of the liquid crystal projector in the first embodimentis 307 mm by 230 mm. The outside size of a conventional liquid crystalprojector not including projecting parts is about 245 mm by about 329mm, and the outside size of the same including a projecting part of itsprojection lens is 245 mm by 380 mm.

The projecting parts of the liquid crystal projector will be describedwith reference to FIG. 3. A liquid crystal projector according to thepresent invention shown in FIG. 3 in a schematic plan view differs fromthe liquid crystal projector shown in FIG. 2 in that the liquid crystalprojector shown in FIG. 3 is provided with a handle 32 and a part of aprojection lens 27 projects from a case 29, whereas the liquid crystalprojector shown in FIG. 2 is not provided with any member correspondingto the handle 32 and has the projection lens 27 entirely contained inthe case 29. The handle 32 can be pulled out from the case 29 to use thesame when carrying the liquid crystal projector. In the presentinvention, the handle 32 and the part of the projection lens 27projecting outside from the case 29 will be called projecting parts.

The outside sizes of liquid crystal projectors according to the presentinvention need not be limited to that of the liquid crystal projector inthe first embodiment shown in FIG. 2 and may be substantially equal tothe A4 folder size. Inquiries into the sizes of A4 folders showed thatthe smallest A4 folder size is 230 mm by 307 mm, a medium A4 folder sizeis 243 mm by 307 mm and the largest A4 folder size is 263 mm by 318 mm.Therefore, the outside size of the liquid crystal projector of thepresent invention may be 263 mm by 318 mm or below. The liquid crystalprojector having an external shape as shown in FIG. 2 can be stored in aprevalently used storage cabinet and can be carried in a prevalentlyused carrying case.

Although it is more technically difficult to form a liquid crystalprojector in a smaller size, a liquid crystal projector having a smallersize enables the use of more kinds of prevalently used storage cabinetsand carrying cases.

The liquid crystal projector in the first embodiment employs liquidcrystal panels having a small screen size to form the liquid crystalprojector in an outside size meeting the foregoing conditions. In theliquid crystal projector in the first embodiment, the screen size of theliquid crystal panels 14, 18 and 21 is 0.9 in., which is smaller than ascreen size of 1.3 in., i.e., the screen size of the liquid crystalpanels employed in the conventional liquid crystal projector. Theprojection lens 27 and the cross dichroic prism 25 may be small and thedimensions of the color separating optical system can be reducedaccordingly when the small liquid crystal panels having a screen size of0.9 in. are employed.

In the prior art liquid crystal projector, the distance between thesurface of the liquid crystal panel and the extremity of the projectionlens is 180 mm, whereas the distance between the display surface of theG liquid crystal panel 18 and the extremity of the projection lens 27 ofthe liquid crystal projector in the first embodiment is 135 mm, and theliquid crystal projector in the first embodiment has a size equal to thesmallest A4 folder size. The distance may be 146 mm or below for aliquid crystal projector of an A4 folder size greater than the smallestA4 folder size because the difference between the longitudinal dimensionof 138 mm of the largest A4 folder size and that of 307 mm of thesmallest A4 folder size is 11 mm.

In the liquid crystal projectors shown in FIGS. 2 and 3, the distancebetween the display surface of the G liquid crystal panel 18 and theextremity of the projection lens 27 is 135 mm. The distance can beincreased to 170 mm if the position of the lamp power supply 31 ischanged.

The liquid crystal projector in the first embodiment is provided with acolor combining optical system including the cross dichroic prism 25 of32 mm by 32 mm in size in a horizontal plane to form the liquid crystalprojector in the A4 folder size. The use of the cross dichroic prism 25of 32 mm by 32 mm or below enables the miniaturization of the colorseparating optical system. A cross dichroic prism employed in the priorart liquid crystal projector is 43 mm by 37 mm in size.

Although the depth of the liquid crystal projector in the firstembodiment is greater than the width of the same, the depth may besmaller than the width.

Referring to FIG. 4 showing a liquid crystal projector in a secondembodiment according to the present invention in a schematic plan view,light rays 2 emitted by a discharge lamp 1, i.e., a light source, arereflected by a parabolic lamp reflector 3, travel through a lens 4, alens 5, a polarizing device 6, a first lens array 7, a mirror 8 and asecond lens array 9, and fall on a dichroic mirror 40. The dichroicmirror 40 reflects R light rays 41 and allows G and B light rays 42 topass through. The R light rays 41 are reflected by a mirror 13 toward anR liquid crystal panel 14. The G and B light rays 42 fall on a dichroicmirror 15 which reflects the G light rays and allows the B light rays topass through. The G light rays 16 are reflected by the dichroic mirror15 toward and fall on a G liquid crystal panel 18. The B light rays 17are reflected by mirrors 19 and 20 toward and fall on a B liquid crystalpanel 21. R transmitted light rays 22 traveled through the R liquidcrystal panel 14, G transmitted light rays 23 traveled through the Gliquid crystal panel 18 and B transmitted light rays 24 traveled throughthe B liquid crystal panel 21 are combined for color combination by across dichroic prism 25, and composite color light rays 26 are projectedthrough a projection lens 27 on a screen, not shown.

An exhaust fan 43 for cooling the discharge lamp 1 is disposed near thedischarge lamp 1 and the lamp reflector 3 to discharge hot air 45 heatedby heat generated by the high-temperature discharge lamp 1, i.e., thelight source, from a case 44 in order that the component parts of theliquid crystal projector may not be affected by heat generated by thedischarge lamp 1. A suction fan 46 sucks ambient air into the case 44. Alamp power supply 31 is disposed near the discharge lamp 1.

The first dichroic mirror 40, the second dichroic mirror 15, the firstmirror 13, the second mirror 19 and the third mirror 20 included in acolor separating optical system are arranged around the cross dichroicprism 25. An illuminating optical system is designed for efficient useof illuminating light and comprises the discharge lamp 1, the lampreflector 3, the lens 4, the lens 5, the polarizing device 6, and anoptical integrating means comprising the first lens array 7, the mirror8 and the second lens array 9. The lamp power supply 31 for supplyingpower to the discharge lamp 1 is disposed adjacent to the discharge lamp1.

In the second embodiment, a linear arrangement of the projection lens27, the cross dichroic prism 25 and the color separating optical system,the illuminating optical system and the lamp power supply 31 arearranged in that order.

When the projection lens 27 is contained in the case 44 and the liquidcrystal projector has projecting parts projecting outside from the case44, the outside size in a horizontal plane of the liquid crystalprojector including the projecting parts is substantially equal to orsmaller than the A4 folder size. The outside size of the liquid crystalprojector in the second embodiment is 230 mm in depth and 307 mm inwidth.

The liquid crystal projector in the second embodiment is formed,similarly to the liquid crystal projector in the first embodiment, inthe outside size suitable for storing the liquid crystal projector in aprevalently used storage cabinet and for carrying the same in aprevalently used carrying case.

In the second embodiment, the projection lens 27 is disposed in thedepth of the case 44. Therefore, the liquid crystal projector can beconstructed so that the distance between the display surface of the Gliquid crystal panel 18 and the extremity of the projection lens 27 issufficiently great. Increase in the distance between the display surfaceof the G liquid crystal panel 18 and the extremity of the projectionlens 27 increases the degree of freedom of design of the projection lensand enables the use of a high-performance projection lens unit. If thewidth of the liquid crystal projector is greater than the depth of thesame, various different layouts of the liquid crystal projector arepossible.

The distance between the display surface of the G liquid crystal panel18 and the extremity of the projection lens 27 is 135 mm in the secondembodiment. If a recess formed in the right side, as viewed in FIG. 4,may be omitted, the distance between the display surface of the G liquidcrystal panel 18 and the extremity of the projection lens 27 can beincreased up to 170 mm.

FIG. 5 shows a liquid crystal projector in a third embodiment accordingto the present invention in a schematic plan view. The liquid crystalprojector in the third embodiment differs from the liquid crystalprojector in the second embodiment shown in FIG. 4 in that, in the thirdembodiment, component parts including an exhaust fan 50 are arranged inan improved layout, and a projection lens 27 is disposed in a frontpart, i.e., a right part as viewed in FIG. 5, of a case 51. The exhaustfan 50 for cooling a discharge lamp 1, i.e., a light source, is disposedat a position near the discharge lamp 1 and a lamp reflector 3 andlaterally dislocated relative to the discharge lamp 1 to discharge hotair 52 heated by heat generated by the high-temperature discharge lamp 1from a case 51 in order that the component parts of the liquid crystalprojector may not be affected by heat generated by the discharge lamp 1.

In the third embodiment, an available space is formed in a back part,i.e., a part on the left side of a color separating optical system asviewed in FIG. 5, of the case 51. The available space increases thedegree of freedom of designing the layout of the component parts ofelectric circuits and enables the use of a high-performance electriccircuits having enhanced functions.

In the liquid crystal projector in the third embodiment, the distancebetween the display surface of the G liquid crystal panel 18 and theextremity of the projection lens 27 is 135 mm. The same distance can beincreased up to 170 mm by shifting the color separating optical systemto the left, as viewed in FIG. 5.

FIG. 6 is a schematic plan view of a liquid crystal projector in afourth embodiment according to the present invention and FIG. 7 is aside view of a liquid crystal panel and a cooling fan included in theliquid crystal projector of FIG. 6.

The liquid crystal projector in the fourth embodiment is provided with acooling system in addition to the components of the liquid crystalprojector in the first embodiment shown in FIG. 2. The cooling systemcomprises a cooling fan 61 disposed beside the projection lens 27 tocool the liquid crystal panels 14, 18 and 21, and a duct for guiding airdelivered by the cooling fan 61 to the liquid crystal panels 14, 18 and21. The cooling system will be described later.

The operation of the liquid crystal projector in the fourth embodimentis similar to that of the liquid crystal projector in the firstembodiment. Illuminating light rays emitted by a discharge lamp 1 areguided by an illuminating optical system to a color separating opticalsystem, the color separating optical system divides the light rays intoR light rays 11, G light rays 16 and B light rays 17, the R light rays11, the G light rays and the B light rays fall on the liquid crystalpanels 14, 18 and 21, respectively. R transmitted light rays 22, Gtransmitted light rays 23 and B transmitted light rays 24 traveledthrough the liquid crystal panels 14, 18 and 21, respectively, arecombined by a cross dichroic prism 25, and composite color light raysprovided by the cross dichroic prism 25 are projected through theprojection lens 27 on a screen, not shown.

An exhaust fan 28 is disposed near a discharge lamp 1 and a lampreflector 3 to discharge hot air 30 outside a case 29 included in theliquid crystal projector. A lamp power supply 31 is disposed near thedischarge lamp 1. The projection lens 27, the cross dichroic prism 25,the color separating optical system, the illuminating optical system andthe lamp power supply 31 are arranged in that order.

The outside size in a horizontal plane of the case 29 of the liquidcrystal projector in the fourth embodiment including projecting parts,if any, is substantially equal to or below the A4 folder size. Theoutside size of the liquid crystal projector in the fourth embodiment is307 mm in depth and 230 mm in width. Since the maximum A4 folder size is263 mm by 318 mm, the liquid crystal projector is formed in an outsidesize not greater than the maximum A4 folder size. The liquid crystalprojector in the fourth embodiment can be stored in a prevalently usedstorage cabinet and can be carried in a prevalently used carrying case.

The liquid crystal panels employed in the liquid crystal projector inthe fourth embodiment formed in the foregoing outside size have a screensize of 0.9 in., which is small as compared with the screen size of 1.3in. of the liquid crystal panels employed in the prior art liquidcrystal projector. Therefore, the projection lens 27 and the dichroicprism may be of small sizes and the color separating optical system canbe miniaturized accordingly.

The cooling fan 61 disposed in a space contiguous with the projectionlens 27 to cool the liquid crystal panels 14, 18 and 21 is a multibladefan, i.e., a centrifugal fan. Cooling air delivered by the cooling fan61 is distributed by a first to a fourth duct (only a first duct 65 anda third duct 70 are shown in FIG. 6) to cool the liquid crystal panels14, 18 and 21. A heatsink 66 is combined with the duct.

Thus, the space contiguous with the projection lens 27 is used forcooling the liquid crystal panels 14, 18 and 21 and the liquid crystalprojector can be formed in the outside size not greater than the A4folder size.

In the liquid crystal projector in the fourth embodiment, the componentparts are arranged such that the distance between the display surface ofthe liquid crystal panel 18 and the extremity of the projection lens 27is 135 mm to form the liquid crystal projector in the outside size notgreater than the A4 folder size. For a greater A4 folder size, thedistance between the display surface of the liquid crystal panel 18 andthe extremity of the projection lens 27 may be 146 mm or below. The sizein a horizontal plane of the cross dichroic prism 25 is 32 mm by 32 mm.The width of the liquid crystal projector may be greater than the depthof the same.

A cooling system according to the present invention will be describewith reference to FIGS. 8, 9 and 10. FIG. 8 is a perspective view of acooling system as viewed from the side of the illuminating opticalsystem in FIG. 6, FIG. 9 is a perspective view of the cooling system asviewed from the side of the extremity of the projection lens 27 in FIG.6, and FIG. 10 is a bottom perspective view of the cooling system.

A cooling fluid, such as air, a gas or a liquid, delivered by thecooling fan 61 flows through the duct 65 toward a space below the liquidcrystal panels 14, 18 and 21 as indicated by the arrow 111 in FIGS. 8and 10. A first guide plate 123, a second guide plate 124 and a thirdguide plate 125 are disposed in the duct 65. The flow of the coolingfluid indicated by the arrow 111 is divided into a cooling fluid flow112 for cooling a B liquid crystal panel 14, a cooling fluid flow 113for cooling a G liquid crystal panel 18 and a cooling fluid flow 114 forcooling an R liquid crystal panel 21 (FIG. 8). The cooling fluid flows112, 113 and 114 are guided toward the liquid crystal panels 14, 18 and21 to cool the liquid crystal panels 14, 18 and 21, respectively. Therespective flow rates of the cooling fluid flows 112, 113 and 114 areadjusted properly by properly arranging the guide plates 123, 124 and125. Generally, the guide plates 123, 124 and 125 are arranged such thatthe flow rates or the velocities of the cooling fluid flow 113 forcooling the G liquid crystal panel 18 which is heated at the highesttemperature among those of the liquid crystal panels 14, 18 and 21, thecooling fluid flow 112 for cooling the B liquid crystal panel 14 whichis heated at the second highest temperature, and the cooling fluid flow114 for cooling the R liquid crystal panel 21 which is not heated at avery high temperature decrease in that order. Thus, the liquid crystalpanels 14, 18 and 21 are heated at substantially the same temperature.The cooling fluid flows through inlets 91 and 92 shown in FIG. 8 and aninlet, not shown, for the R liquid crystal panel 21 in directionsindicated by the arrows 115 and 116 to cool the liquid crystal panels14, 18 and 21.

As shown in FIG. 9, the cooling fluid flows further through a secondduct 101, and the heat of the cooling fluid is absorbed and dissipatedby a heatsink 66 attached to a wall of the second duct 101 while thecooling fluid flows through the second duct 101. The cooling fluid flowsfurther through a third duct 70 and a fourth duct 71 and returns to thecooling fan 61. The first duct 65, the second duct 101, the third duct70 and the fourth duct 71 form a cooling fluid circulating passage, andthe liquid crystal panels 14, 18 and 21 and the cooling fan 61 aresealed in the cooling fluid circulating passage. Therefore foreignmatters are unable to enter the cooling fluid circulating passage andthe undesirable projection of images of dust particles adhering to thedisplay surfaces of the liquid crystal panels 14, 18 and 21 can beavoided. The first duct 65, the second duct 101, the third duct 70 andthe fourth duct 71 need not necessarily be connected so as to form asealed cooling fluid circulating passage. The cooling system may beprovided with only the first duct 65 and the display surfaces of theliquid crystal panels 14, 18 and 21 may be covered with glass plates,respectively, to prevent troubles attributable to dust adhering to thedisplay surfaces of the liquid crystal panels 14, 18 and 21.

In the cooling system embodying the present invention, the flow of thecooling fluid delivered by the cooling fan 61 is divided by the guideplates 123, 124 and 125, three pipes or the like may be used for thesame purpose instead of the guide plates 123, 124 and 125.

FIG. 11 shows a liquid crystal projector in a fifth embodiment accordingto the present invention in a schematic plan view. The liquid crystalprojector in the fifth embodiment is similar to the liquid crystalprojector in the second embodiment and differs only in that the liquidcrystal projector in the fifth embodiment is provided additionally witha cooling system. The cooling system comprises a cooling fan 61 disposedbeside a projection lens 27 to deliver air for cooling liquid crystalpanels 14, 18 and 21, and a duct for guiding air delivered by thecooling fan 61 to the liquid crystal panels 14, 18 and 21.

The liquid crystal projector in the fifth embodiment operates similarlyto the liquid crystal projector in the second embodiment. A dischargelamp 1 emits illuminating light rays, the illuminating light rays areguided by an illuminating optical system to a color separating opticalsystem, and the color separating optical system separates theilluminating light rays into R light rays 41, G light rays 16 and Blight rays 17 so that the R light rays 41, the G light rays 16 and the Blight rays 17 fall on liquid crystal panels 14, 18 and 21. R transmittedlight rays 22, G transmitted light rays 23 and B transmitted light rays24 traveled through the liquid crystal panels 14, 18 and 21 are combinedfor color combination by a cross dichroic prism 25 and composite lightrays are projected by a projection lens 27 on a screen, not shown.

An exhaust fan 43 for cooling a light source is disposed near adischarge lamp and a lamp reflector 3 to discharge hot air 45 outside acase included in the liquid crystal projector. A lamp power supply 31 isdisposed near the discharge lamp 1. A linear arrangement of theprojection lens 27, the cross dichroic prism 25 and the color separatingoptical system, the illuminating optical system and the lamp powersupply 31 are arranged in that order.

In the liquid crystal projector shown in FIG. 11, a cooling fan 61,similarly to the cooling fan 61 employed in the fourth embodiment, isdisposed beside the projection lens 27. The basic constitution of thecooling system is the same as that illustrated in FIGS. 8, 9 and 10. Thecooling fan 61 disposed near the lamp reflector 3 is subject to theinfluence of heat and must be protected by a heat insulating plate 60 orthe like. The effect of the fifth embodiment in being formed in acompact construction and in a small height is the same as that of thefourth embodiment.

The liquid crystal projector may be formed in a construction in whichall the component parts thereof including the projection lens 27 arecontained in a case 44 as shown in FIG. 11, or may be formed in aconstruction in which projecting parts, such as a projecting part of theprojection lens 27, a handle and the like, projects from the case 44.The outside size in a horizontal plane of the liquid crystal projectorin either construction is not greater than the A4 folder size. Theliquid crystal projector in the fifth embodiment is 230 mm in depth and307 mm in width. The size in a horizontal plane of the cross dichroicprism 25 is 32 mm by 32 mm. The distance between the display surface ofthe liquid crystal panel 18 and the extremity of the projection lens 27is 135 mm.

The liquid crystal projector in the fifth embodiment, similarly to theliquid crystal projector in the second embodiment, can be stores in aprevalently used storage cabinet and can be carried in a prevalentlyused carrying case.

In the fifth embodiment, the projection lens 27 is disposed in the depthof the case 44. Therefore, the liquid crystal projector can beconstructed so that the distance between the display surface of theliquid crystal panel 18 and the extremity of the projection lens 27 issufficiently great. Generally, increase in the distance between thedisplay surface of the liquid crystal panel 18 and the extremity of theprojection lens 27 increases the degree of freedom of design of theprojection lens and enables the use of a high-performance projectionlens.

FIG. 12 shows a liquid crystal projector in a sixth embodiment accordingto the present invention in a schematic plan view. The liquid crystalprojector in the sixth embodiment differs from that in the fifthembodiment in that, in the sixth embodiment, component parts includingan exhaust fan 50 are arranged in an improved layout, and a projectionlens 27 is disposed in a front part of a case 51. The exhaust fan 50 forcooling a light source is disposed at a position near a discharge lamp 1and a lamp reflector 3 and laterally dislocated relative to thedischarge lamp 1 to discharge hot air 52 heated by heat generated by thehigh-temperature discharge lamp 1 from the case 51 in order that thecomponent parts of the liquid crystal projector may not be affected byheat generated by the discharge lamp 1.

In the sixth embodiment, a cooling fan 61 is disposed beside theprojection lens 27 on one side of the projection lens 27 opposite theother side on which a lamp reflector 3 is disposed. to cool liquidcrystal panels 14, 18 and 21 efficiently without being affected by heatradiated from the lamp reflector. A cooling system for cooling theliquid crystal panels 14, 18 and 21 in the sixth embodiment issubstantially the same in basic construction as that of the fifthembodiment and is in inverse positional relation with that of the fifthembodiment. Further, as the exhaust fan 50, blower fan 50A may be usedas shown in FIG. 12.

An available space is formed in a back part of the case 51, whichincreases the degree of freedom of designing the layout of electricalparts for electric circuits and enables the use of a high-performanceelectric circuits having enhanced functions. The liquid crystalprojector in the sixth embodiment is 230 mm in depth and 307 mm inwidth. The size in a horizontal plane of a cross dichroic prism 25employed in the sixth embodiment is 32 mm by 32 mm, and the distancebetween the display surface of the liquid crystal panel 18 and theextremity of the projection lens 27 is 135 mm.

In any one of the foregoing embodiments, the optical system includes atleast the illuminating optical system and the color separating opticalsystem, and is provided additionally with the liquid crystal panels andthe cross dichroic prism. The projection unit comprises the projectionlens, the liquid crystal panels and the cross dichroic prism.

As is apparent from the foregoing description, according to the presentinvention, the outside size in a horizontal plane of the liquid crystalprojector including the projecting parts at least in a folded state isnot greater than the A4 folder size and hence the liquid crystalprojector can be stored in a prevalently used storage cabinet and can becarried in a prevalently used carrying case. The cooling space can bedisposed in a small space, the plurality of liquid crystal panels arecooled properly at substantially the same temperature according to therespective heat generating rates thereof.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsare therefore to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than by the foregoing description and all changes whichcome within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

1. A liquid crystal projector comprising: a liquid crystal panel; aprojection lens; a cooling fluid circulating system having a centrifugalcooling fan disposed at one lateral side of said projection lens and asealed duct including said liquid crystal panel; a cooling system forcooling said sealed duct from outside disposed at another lateral sideof said projection lens; and a housing having said liquid crystal panel,said projection lens, said cooling fluid circulating system and saidcooling system disposed entirely therein, wherein said cooling fluidcirculating system cools said liquid crystal panel directly, and saidcooling system cools said liquid crystal panel indirectly.
 2. The liquidcrystal projector according to claim 1, wherein said cooling fluidcirculating system is provided with said centrifugal cooling fan usedspecially for cooling said liquid crystal panel.
 3. The liquid crystalprojector according to claim 2, wherein said sealed duct comprises afirst duct and a second duct, and said cooling fluid is caused by saidcentrifugal cooling fan to pass through said first duct, said liquidcrystal panel, and said second duct and returns to said centrifugalcooling fan.
 4. The liquid crystal projector according to claim 3,wherein said cooling system comprises a heat sink.
 5. A liquid crystalprojector comprising: a plurality of liquid crystal panels; a projectionlens; a cooling fluid circulating system having a centrifugal coolingfan disposed at one lateral side of said projection lens and a sealedduct including said plurality of liquid crystal panels; a cooling systemfor cooling said sealed duct from outside disposed at another lateralside of said projection lens; and a housing having said liquid crystalpanel, said projection lens, said cooling fluid circulating system andsaid cooling system disposed entirely therein, wherein said coolingfluid circulating system cools said plurality of liquid crystal panelsdirectly, and said cooling system cools said plurality of liquid crystalpanels indirectly.
 6. The liquid crystal projector according to claim 5,wherein said first cooling fluid circulating system is provided withsaid centrifugal cooling fan used specially for cooling said pluralityof liquid crystal panels.
 7. The liquid crystal projector according toclaim 6, wherein said sealed duct comprises a first duct and a secondduct, and said first cooling fluid is caused by said centrifugal coolingfan to pass through said first duct, said plurality of liquid crystalpanels, and said second duct and returns to said centrifugal fan.
 8. Theliquid crystal projector according to claim 7, wherein said coolingsystem comprises a heat sink.
 9. A liquid crystal projector comprising:a plurality of liquid crystal panels; a projection lens; a cooling fluidcirculating system having a cooling fan disposed at one lateral side ofsaid projection lens and a sealed duct including said plurality ofliquid crystal panels, said cooling fan being used specifically forcooling said plurality of liquid crystal panels and said duct comprisinga first duct and a second duct, and said cooling fluid is caused by saidcooling fan to pass through said first duct, said liquid crystal panel,and said second duct and returns to said cooling fan; a cooling systemfor comprising a heat sink for cooling said sealed duct from outsidedisposed at another lateral side of said projection lens; and whereinsaid first duct has guide members in the inside and said guide membersdivide said cooling wind and supply said divided cooling wind to each ofsaid plurality of liquid crystal panels; a housing having said pluralityof liquid crystal panels, said cooling fluid circulating system and saidcooling system mounted therein; and wherein said cooling fluidcirculating system cools said plurality of liquid crystal panelsdirectly, and said cooling system cools said plurality of liquid crystalpanels indirectly.
 10. A liquid crystal projector comprising: aplurality of liquid crystal panels; a projection lens; a cooling fluidcirculating system having a cooling fan disposed at one lateral side ofsaid projection lens and a sealed duct including said plurality ofliquid crystal panels; a cooling system for cooling said sealed ductfrom outside disposed at another lateral side of said projection lens;and a housing having said liquid crystal panel, said cooling fluidcirculating system and said cooling system mounted therein, and whereinsaid cooling fluid circulating system cools said plurality of liquidcrystal panels directly, and said cooling system cools said plurality ofliquid crystal panels indirectly, and further comprising a plurality ofguide members disposed in said duct and for dividing a cooling fluiddelivered by said cooling fan into plural cooling fluid flows forcooling each of said plurality of liquid crystal panels respectively,one of the plural cooling fluid flows having a greater flow rate or avelocity than another plural cooling fluid flow.